A magnetic circuit intended to utilize the magnetostrictive properties of a giant magnetostrictive material is disclosed, inter alia, in PCT patent application WO 86/03888 entitled "A rare earth flextensional transducer". The movement of the transducer is here brought about with the aid of a number of basic elements, stacked in a row one after the other, each element consisting of a rod or a giant magnetostrictive material. The rod is magnetized with a surrounding coil and is, in addition, bias magnetized with the aid of permanent magnets positioned at both ends.
Another example of a magnetic circuit including rods of a giant magnetostrictive material is disclosed in British patent application GB 2 174 863 A entitled "Permanent magnet biased magnetostrictive transducer". Here four basic elements, each being rotated 90.degree. in relation to one another, form a square shape. The rod in each basic element is also here surrounded by a magnetizing coil outside of which permanent magnets for the bias magnetization are arranged.
It is obvious that the efficiency of the known magnetic circuits leaves a great deal to be desired because of the great leakage fluxes arising. This also results in the magnetic flux in the rods not becoming as homogeneous as is desirable to obtain maximum power caused by the magnetostriction.